Mesogen phase correlations

Fig. 7.15. Mesogen phase correlations using well-characterized siloxanes (After...

Fig. 8.53 Phases of HHTT K= microcrystalline H = mesogenic, long-range order with a correlation length > 800 A Dh = mesogenic phase / = isotropic phase. From [55].

One of the primary features of the Gay-Berne potential is the presence of anisotropic attractive forces which should allow the observation of thermally driven phase transitions and this has proved to be the case. Thus using the parametrisation proposed by Gay and Berne, Adams et al. [9] showed that GB(3.0, 5.0, 2, 1) exhibits both nematic and isotropic phases on varying the temperature at constant density. This was chosen to be close to the transitional density for hard ellipsoids with the same ellipticity indeed it is generally the case that to observe a nematic-isotropic transition for Gay-Berne mesogens the density should be set in this way. The long range orientational order of the phase was established from the non-zero values of the orientational correlation coefficient, G2(r), at large separations and the translational disorder was apparent from the radial distribution function. 

Fig. 8. The distance dependence of the bond orientational correlation function gs (r ) found for the mesogen GB(4.4, 20.0, 1, 1) in the smectic A (.) and the smectic B (—) phases...

The liquid crystal phases of calamitic mesogens fall into two types - nematic (N) and smectic (Sm). The nematic phase is the most disordered of the liquid crystal phases and possesses only orientational order, so that the long axes of the molecules are correlated in one direction (known as the director, n) while being positioned randomly (Fig. 2A). There are several smectic phases and these differ from the nematic phase in possessing partial posi-... 

It is well-established that solutes incorporated in liquid crystalline phases are oriented in a manner and to an extent that depends primarily on structural similarities between the solute and the mesogen (2a-b,3-8). The rotational and diffusive mobility of both the solute and the mesogen is rendered strongly anisotropic, an effect that also correlates (for the former) with solute/mesogen structural similarities. 

Gottke et al. [5] offered a theoretical treatment of collective motions of mesogens in the isotropic phase at short to intermediate time scales within the framework of the Mode coupling theory (MCT). The wavenumber-dependent collective orientational time correlation function C/m(, t) is defined as... 

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